It is known that atrial ventricular blockages are today cured easily by means of an electrical cardiac stimulator or artificial pacemaker which, through an electrode inserted in the cardiac muscular tissue of the ventricle, transmits, to the heart, continuously and with the same rhythm, electrical stimuli capable of making the heart beat regularly. It has been proven that persons wearing an artificial pacemaker, especially if it is implanted subcutaneously and provided with long-lasting batteries, have a work capacity not significantly lower than normal, even with respect to activities which require muscular effort.
The limits to the muscular effort which can be exerted by wearers of artificial pacemakers are today imposed by the impossibility, on the part of the pacemaker, to self-regulate the frequency of the stimuli delivered and, consequently, of the heart beat, more especially to increase the cardiac output in response to the increased metabolic requirements of the body.
It is a known fact that, when a person exerts an effort, the body presents a hemodynamic picture characterized by the following:
A. THE HEART INCREASES ITS BEAT FREQUENCY UP TO DOUBLE THE USUAL FREQUENCY AND TRIPLE THE FREQUENCY, IN LINEAR AND DIRECT RATIO TO GIVEN VALUES, AS THE INTENSITY AND DURATION OF THE PHYSICAL EFFORT INCREASES;
B. WITHIN A CERTAIN FREQUENCY OF THE CONTRACTIONS, THE HEART INCREASES THE SYSTOLIC OUTPUT AS THE PHYSICAL EFFORT INCREASES, THE INCREASE IN FREQUENCY OF CONTRACTIONS AND THE INCREASE IN SYSTOLIC OUTPUT COMBINING TO INCREASE THE CARDIAC OUTPUT SO AS TO FURNISH THE OXYGEN REQUIREMENTS; AND
C. THE PERIPHERAL RESISTANCES, AND THUS ALSO THE SYSTOLIC PRESSURE, INCREASE.
The body, when exerting a physical effort, also presents a metabolic picture with the increase in muscular efforts, as follows:
A. THE LACTIC ACID INCREASES;
B. THE PCO.sub.2 increases;
C. THE PO.sub.2 decreases in the arterial blood; and
D. THE HYDROGEN ION CONCENTRATION INCREASES IN THE CORONARY, VEINOUS AND ARTERIAL BLOOD, WHICH IS EQUIVALENT TO A REDUCTION OF THE PH.
Considering now a subject with stable atrio-ventricular block, or with atrial-ventricular block controlled by an artificial pacemaker of fixed frequency, the metabolic picture presents more marked variations, since the hemodynamic picture is deficient due to the fact that the cardiac output increases only a little and with difficulty, through the increase in systolic pressure alone, with the result of early fatigue and the impossibility of continuing the physical effort.